It is known to treat textile and other webs with a heated gaseous treating agent upon the cylindrical perforated periphery of a drum which is associated with a blower or the like to force the gaseous treating agent in substantially radial direction against the cylindrical surface of the drum. The treating medium traverses the ports or perforations of the cylindrical drum surface upon which the material lies in a fully supported and hence untensioned manner.
Such devices have been described, for example, in British patent No. 1,216,980 in which the apparatus is a so-called drum dryer. In this case, the treating agent, e.g. hot air, serves to dry the textile web.
German patent DT-PS No. 1,604,770 discloses a predrying path ahead of the drum dryer so that liquids which may be entrained with the textile webs do not come into contact with the perforated drum periphery. In other words, a major part of the adherent liquid is removed in the predrying stage so that only residual moisture must be eliminated on the periphery or surface of the drying drum. These conventional systems have the disadvantage that the transfer of the web to the surface of the drum and/or the transport of the web over the predrying path ahead of the drum is not tension-free and hence may result in distortion of the web. A tension-free drying of a textile web is desirable where the web is only loosely coherent and hence is subject to being torn apart by the transfer to the web or along a predrying path, especially since the weight of the exit web is often considerable.